Biopsy

Where diagnosis is unclear but there is a differential diagnosis, an ellipse of skin can be taken through the edge of a lesion. There is a need to ensure that normal and abnormal skin (epidermis, dermis and fat) are included in the sample. Incisional, excisional and punch biopsies may be taken. Punch biopsies provide only limited sample, which may be inadequate for histological examination. Typically, the punch biopsy includes the full thickness skin and subcutaneous fat in the diagnosis of skin diseases. A round-shaped knife ranging in size from 1–8 mm is taken. The smaller size punch (1 mm) helps to minimise bleeding and assists in the vhealing of the wound without stitching. To diagnose many inflammatory skin conditions, the common punch size used is the 3.5- or 4-mm punch.